This invention relates to coated polyester fibers which are indigo-dyeable and possess wash-down and crocking resistance characteristics similar to indigo-dyed cotton fibers and to a process for preparing such fibers.
Indigo-dyed denim fabrics are twill fabrics in which only the warp yarns are dyed. For reasons of style, it is desired not only that these fabrics have an initial deep indigo blue color, but also that the fabrics begin to fade in an obvious manner after only a few wearings and launderings. For stronger, more durable fabrics with better fabric stability than all-cotton fabrics, blends of polyester staple fibers with cotton have been used. The undyed filling yarns can be made of 50/50 polyester/cotton blends for high strength. However, since commercially available polyester fibers will not dye with indigo, it has been found that the warp yarns can contain only a small amount of polyester fibers--only about 10 wt. % in open-end-spun yarns and no more than about 25 wt. % in ring-spun yarns--if the desired deep blue color is to be obtained. At higher blend levels, it becomes increasingly difficult to make a fabric which can be dyed to an acceptable indigo shade.
The use of polyaminoalkylsilanes to coat either natural or synthetic fibers so that they will be dyeable with a wide variety of dyestuffs has been disclosed by Speier in his U.S. Pat. No. 3,504,998. The polymerization of unsaturated compounds containing polyalkylene oxide segments onto polyester, polyamide, and polyacrylonitrile fibers to provide them with indigo-dyeable surfaces is described by Toray Industries, Inc., in their Japanese patent application (Kokai) 77778/79. However, polyester staple fibers adapted for indigo dyeability with wash-down and fading characteristics adequately simulating indigo-dyed cotton fibers have not been described by the prior art.